The present invention relates to a method of and an apparatus for controlling the temperature of a die in a low-pressure casting process, and more particularly to a method of and an apparatus for controlling the temperature of a die in a low-pressure casting process by detecting die temperatures respectively in the various steps of a casting cycle which include a step from the clamping of the die to the starting of pouring molten metal into the die, a step of filling the molten metal in the die, and a step after the filling of the molten metal until the opening of the die, and by controlling the cooling of the die according to an optimum cooling pattern, so that the quality of the cast product will be stable and high irrespective of different casting cycles which the die undergoes.
Generally, the low-pressure casting process is widely employed for mass-producing automotive parts or the like. In the low-pressure casting process, molten light alloy (hereinafter referred to as "molten metal") such as an aluminum alloy or the like is heated and held in a sealed container, and the surface of the molten metal in the container is pressurized by an inert gas or air under a relatively low pressure to force the molten metal via a feed pipe into a die cavity defined in a die for casting a product.
During the low-pressure casting process, cooling water is supplied to the die to control the temperature of the die which is associated with a temperature sensor. When the actual temperature of the die as detected by the temperature sensor is higher than a reference temperature, cooling water is supplied to the die. When the detected die temperature is lower than the reference temperature, the supply of cooling water is stopped. In this manner, the temperature of the die is kept in a certain temperature range.
The casting machine for carrying out the casting process necessarily has certain downtimes when the casting is removed after the die has been opened when the die is cleaned after the casting has been taken out, and when sand cores are set in the die. One casting cycle may also be interrupted by a trouble with the die or a trouble caused by an erroneous action of the operator. Usually, therefore, the casting process contains different or irregular casting cycle.
If the intervals between the steps of pouring molten metal into the die in the respective different casting cycles differ from each other, then the initial temperatures of the die when starting to pour the molten metal also differ from each other in the respective casting cycles. The different initial temperatures in the respective casting cycles result in different patterns in which the temperatures of the die and the molten metal vary in the stage of filling the molten metal in the die cavity and solidifying the molten metal under pressure.
The aforesaid temperature control method cannot effectively cope with varying conditions in the different casting cycles. More specifically, cooling water is supplied or interrupted solely based on the reference die temperature regardless of how each casting cycle proceeds through the steps thereof. Since the temperature conditions of the die in the respective casting cycles are not constant, the castings produced by the casting process do not have uniform quality, and sometimes defective castings may be produced because of unexpected conditions resulting from the different casting cycles.